Shell implementation of a simple calculator function small script

Nonsense not much to say, directly on the code, the basic implementation of subtraction functions:

#!/bin/bash# author by alsww# date : 2016.02.03# mail : [email  protected]# blog : alsww.blog.51cto.comprint_info () {    printf  " Please enter the number: \ n "}print_err_num () {    printf " Please enter the correct number!\n "}print_err_fuhao () {     printf  "Please enter the correct operation symbol (+ - * /): \ n"}while :d O    read  -p  "Please enter the first digit:"  num1    echo  $num 1|grep -q  ' ^[-]\? [0-9]\+$ '  && break | |  print_err_numdonewhile :d o    read -p  "Please enter an operator (shaped like  :+ -  * /): " ysf    if [ " $YSF " != " + " ]&&[   "$YSF"  !=  "-"  ]&&[  "$YSF"  !=  "*"  ]&&[  "$YSF"  !=  "/"  ]    then        print_err_fuhao    else        break     fidonewhile :d o    read -p  "Please enter the second digit:"  num2     echo  $num 2|grep -q  ' ^[-]\? [0-9]\+$ '  && break | |  print_err_numdoneecho  "Operation Result: ${num1}${ysf}${num2}=$ ((${num1}${ysf}${num2}))  "

Effect:

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Shell implementation of a simple calculator function small script